[Python] Ch1: Python Basics - 01 Python Basics

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Python Basics

Interactive Shell

Compiled language v.s. Interpreted language

  • Compiled language (編譯語言)

    Through compiler convert source code into machine code and execute it.

    • C/C++
    • Go
    • Rust

  • Interpreted language (直譯語言)

    Execute the code step-by-step.

    • Python
    • JavaScript
    • Ruby
    • PHP

Python Interactive Shell

Python is a Interpreted language. It means it excutes the code line by line.

Python provides a Python Shell (Python Interactive Shell) which is used to execute a single Python command and get the result.

  1. Open terminal
# or python3
$ python
  1. Then you will see the figure below

  1. Now, you can type a single statement and get the result

Python Comments

Comments can be used to explain code, make the code more readable.

  • #: single line
  • """ """: multiple lines

Examples:

# This is a comment
print('Hello world')

"""
This is a comment
written in more than just one line
"""
print('Hello world')

Python Expressions: Math Operators

# Addition: Integer
2 + 3 # 5

# Addition: Floating point & Floating point -> Floating point
2.0 + 3.0 # 5.0

# Addition: Floating point & Integet -> Floating point
2.0 + 3 # 5.0

# Multiplication
3 * 2 # 6

# Exponent
2 ** 5 # 32

Exercise

Suppose you have $100, which you can invets with a 10% return each year.
After one year, it's 100 x 1.1 = 110 dollars,
and after two years it's 100 x 1.1 x 1.1 = 121.

Add code to calculate how much money you end up with after 7 years, and print the result.

# Click below for a solution

return_money = 100 * (1.1 ** 7)
return_money

[Out]: 194.87171000000012

Display the Output

Builtin-in function print() serves as an output statement in Python.

# type 1.
print("Hello World!")

# type 2.
print("Hello" + " World1")

# type 3.
text = "world!"
print("Hello", text)

# type 4.
text = "world!"
print("Hello {}".format(text))

Hello World!
Hello World1
Hello world!
Hello world!

Getting the User’s Input

The input() function is part of the core library of standard Python distribution.

It reads the key strokes as a string object which can be referred to by a variable having a suitable name.

_input = input()

print("input: {}, type: {}".format(_input, type(_input)))

123
input: 123, type: <class 'str'>

name = input("Enter your name: ")
print("Welcome, {}".format(name))

Enter your name: kaka
Welcome, kaka

Variables

Variables are containers for storing data values. In order to conveniently repeatedly refer to the store value, it is given a suitable name.

  • Specific, case-sensitive name
  • Call up value through variable name

A value is bound to a name by the assignment operator =

Example

Height 1.75m, Weight 68.7kg, Calculate BMI

height = 1.75
weight = 68.7

bmi = weight / (height ** 2)
print("BMI: {}".format(bmi))

Data Types

Variables can store data of different types, and different types can do different things.

A data type is a category for values, and every value belongs to exactly one data type.

Python has the following standard or built-in data types:

Numeric

  • Integets (int): 1, 0, 1
  • Float (float): -1.25, -0.5, 0.0, 1.25
  • Complex (complex): 1j

Boolean

Data with one of two built-in values True or False.

Sequence

  • Strings (str):

    String literals in python are surrounded by either single quotation marks, or double quotation marks.

    ‘Hello’ is the same as “Hello”.

    Example:

    a = 'Hello Wrold!'

  • list:

    List is a collention which is ordered and changeable. Allow duplicate members.

    Example:

    a = ['Hello', 'World', '!']

  • tuple: Tuple is a collention which is ordered and unchangeable. Allow duplicate members.

    Example:

    a = ('Hello', 'World', '!')

Dictionary

Dictionary is a collention which is unordered, changeable and indexed. No duplicate members.

Example:

a = {"name": "kaka", "age": 28}

Storing Values in Variables

Assignment

在程式語言的世界裡，=代表的是指定(assignment)的意思

例如：x = 7 就是把7這個物件指定給x這個變數，換句話說也就是把x這個變數指向(綁定)7這個物件，如下圖所示：

x = 7
x

[Out]: 7

x = 7
y = x
y

[Out]: 7

x = 8
print("x =", x, "y =", y)

[Out]: x = 8 y = 7

Pyhton Assignmes: Bindding

# Fist, we see an example as below:
x = [1, 2, 3]
y = x
x[1] = 100
print("x: ", x)
print("y: ", y)

x:  [1, 100, 3]
y:  [1, 100, 3]

Explain

Python的=實際上是 binds an object reference to an object

x = [1, 2, 3]

X ----> [1 2 3]

y = x

x ---> [1 2 3]
       ^
       |
y ------

x[1] = 100

x ---> [100 2 3]
       ^
       |
y ------

Your First Program

# This program says hello and asks for my name and age.
print('Hello World!')
print('What is your name?')
print('------------------')
name = input()
print('It is good to meet you, ' + name)
print('The length of your name is: ', len(name))
print('What is your age?')
age = input()
print('------------------')
print('You will be ' + str(int(age) + 1) + ' in a year')

Hello World!
What is your name?
------------------
kaka
It is good to meet you, kaka
The length of your name is:  4
What is your age?
28
------------------
You will be 29 in a year

Kaka LinSoftware Engineer

AIoT